1. Field of the Invention
The present invention relates generally to a variable valve timing arrangement for an internal combustion engine and more specifically to a rocker arm construction for such an arrangement.
2. Description of the Prior Art
JP-A-63-167016 and JP-A-63-57805 disclosed rocker arm arrangements which include a first rocker arm which is arranged to cooperate with a low speed cam and a second rocker arm which cooperates with a high speed cam. The two rocker arms pivotally mounted on a common rocker arm shaft.
A hydraulically operated connection device which enables the first and second rocker arms to be selectively locked together, comprises a set of plunger bores which are formed in the rocker arms in a manner to be parallel with and at a predetermined distance from the axis of the shaft about which the arms are commonly pivotal. By applying a hydraulic pressure to the end or ends of the plungers reciprocally disposed in the bores, the plungers can be induced to move axially within their bores and induce the situation wherein two of the plungers will partially enter an adjacent bore and lock the two arms together.
However, this arrangement has suffered from the drawbacks that as the rocker arms are pivotally mounted on a rocker arm shaft minor variations in the rocker arm dimensions lead to variations in the opening and closing timing of the engine valves; and in that the rocker arms become relatively large and exhibit large moments.
In addition to this, seats for the lost motion springs which are operatively connected with the high speed rocker arms must be provided on the cylinder head. This of course increases the complexity of forming and arranging the upper surface of the cylinder head.